The present invention relates to a compact power generation apparatus according to the preamble of claim 1. The invention further relates to a method of generating energy, a method of automated power management of a compact power generation apparatus, and a power management system for carrying out this method.
Small generators and accessories such as small heaters and battery chargers are products which are used in a wide field of applications. Such type of small generator can be used for powering a heater and other electrical appliances in e.g. trucks, leisure boats, mobile homes, caravans, for military purposes, in crises zones and other areas where normal electrical power and heat sources are not available,
The generator is driven by an internal combustion engine for the generation of electrical power. This power can be used for powering various electrical devices, such as electrical heaters, lights, pumps, etc. and air conditioning installations.
The combustion engine in the generator can be air cooled, such as e.g. known from GB-A-2 213 201, U.S. Pat. No. 4,835,405, U.S. Pat. No. 4,608,946 or DE-A1-35 11 123. A constant flow of air is generated around the engine and the generator in order to remove the surplus heat, preventing the engine and the generator from overheating. The flow passages of the cooling air are designed in such a way that the noise from the engine is reduced. Also a silencer such in the exhaust is installed, and a protective, soundproof cover is fitted around the unit, in order to reduce the noise emission from the generator unit. Most devices are controlled by regulating the revolutions per minute of the engine and thus the frequency of the output. A small fuel tank is installed allowing for a few hours of operation. An exhaust silencer is fitted for noise reduction purposes.
For the provision of heat, heaters are known that consist of a hot chamber in which the fuel is consumed and a fin provides air for the combustion. A small fuel pump which is controlled by basic control electronics control the amount of fuel. The associated control panel is typically a timing device, which will allow a timed start and stop.
Battery chargers normally consist of a transformer which is designed such that when a certain charging voltage has been reached, the current will be close to zero and thus providing a simple charging mechanism. Unfortunately, the point where a battery is considered fully charged varies considerably with the temperature and rarely the batteries are charged properly causing a substantial wear on the batteries and a low life time.
In boats, trucks, mobile homes etc. the increasing power consumption due to the increase in the amount of equipment such as micro wave ovens, heaters, television, etc. require large battery capacity and large battery chargers in order to provide adequate battery charging when power is available.
In trucks for example, the need for battery charging, air conditioning and heating, when the main engine is not running, is real. The heating can be solved by using a small diesel powered heater which consumes considerable DC power when in use and thus increases the need for battery charging even more. Air conditioning is only possible to have while the main engine is running and truck drivers must tolerate ambient temperatures when resting.
From e.g. U.S. Pat. No. 5,433,175 an engine generator is known where a water cooled diesel engine for driving the generator. The use of water as coolant provides an efficient cooling in a compact system, just as the water cooling system in addition provides a noise reducing effect. Other water cooled diesel solutions are also known in particular for maritime purposes, that exhibits an excellent noise reduction and thus an extremely silent and compact generator.
However, these water cooled generators generally have a low efficiency. Moreover, a water cooling system is quite heavy as water connections, flow channels and air coolers must be present. This makes the water cooled generators both heavy and somewhat bulky and thus less suitable for purposes where frequent transportation is needed.
The low efficiency is a rather generic problem by an engine as well as by a generator. In the conversion from one energy source to another, energy is lost. In the engine where the fuel is combusted, in the transmission between the engine and the generator and in the conversion of mechanical energy into electrical power in the generator. Insufficient cooling and poor air supply and circulation into and around the engine are also factors contributing to a poor overall performance of a power generation apparatus. However, the reduction of the noise emission of the small generator usually causes some amount of decrease in efficiency of the power output, although many solutions attempts to minimise this efficiency decrease.
The efficiency is also decreased in the subsequently connected electrical appliances, and current small diesel powered generators only convert 20-30% of the total available power into electrical power. The remaining energy in the form of heat is wasted.
The object of the present invention is to provide a solution to these above identified problems and other problems associated with the prior art solutions and to provide a compact power generation apparatus. It is a further object of the invention to provide a method of generating energy and managing the power generation in a compact power generation apparatus.
This object is achieved by a compact power generation apparatus of the initially mentioned kind, wherein heat exchanging means are provided for extracting heat from the exhaust system and from the circulating air flow and passing said extracted heat on to a utility medium, such as air or water for utility purposes.
By the present invention a compact power generation apparatus is provided that can produce several types of energy outputs for the consumption in e.g. cabins of trucks, boats and recreation vehicles. By producing both electrical and heat energy for the consumption, the electrical energy need not be converted further in order to produce heat. This means that the efficiency in the production of heat is improved compared to the generator-sets known in the art. The heat energy that previously was considered a waste produce, can now be recovered and used for e.g. heating purposes, such as hot water or hot air. By cooling the exhaust air, the air volume is reduced and thus the noise level is reduced.
By making use of the available energy, including the normally wasted heat, the efficiency of a compact power generation apparatus according to the invention can be increased immensely.
In the preferred embodiment of a compact power generation apparatus according to the invention, the flow generating means involves means for generating an air flow through the generator, the engine and/or the heat exchanging means. This ensures a sufficient amount of air supply for the engine to run smoothly and a good cooling effect.
In the preferred embodiment the housing is provided with an inner and an outer chamber, said chambers being connected by a spacing divided into channels, said inner chamber accommodating the engine, generator and heat exchanging means. The channels between the inner and outer chamber can moreover be covered in sound absorbing material. Hereby a good cooling air circulation is provided that also provides a noise reduction of the power generation apparatus.
The inner chamber is in a preferred embodiment diverted into a number of channels, in which the cooling air can circulate by the assistance of a first and second fan that are provided in the inner chamber, in such a way that the inner chamber exhibits a cool section between the two fans and a hot section after the second fan. Hereby an efficient cooling is provided by the circulating air. By providing a slight over pressure in the cold section where the air intake is located, a super charging effect can be provided for the engine.
In the preferred embodiment, the first fan is a fly wheel mounted on the shaft of the generator forcing air through and around the generator. The second fan is preferably mounted by the air intake of the engine, preferably as a part of the fly wheel of the engine, and the first and second fan are so dimensioned that an relative higher pressure than the ambient pressure is present in the cold section. This solution provides an satisfactory air circulation in a simple manner.
The heat exchanging means in a power generation apparatus according to the invention comprises in the preferred embodiment of the invention, a first heat exchanger and second heat exchanger, the first heat exchanger extracting the heat from the exhaust system and heating the circulating cooling air, and the second heat exchanger separating the heat from the hot circulating air, and fresh air. The first heat exchanger could preferably be an exhaust silencer, possibly in a design where a substantial flow resistance in the exhaust is present in such a way that the design is suitable for extracting the heat from the exhaust. By the two heat exchangers the heat can safely be extracted from both the exhaust and the hot utility air, i.e. both the air that flows through and around the engine and the generator. By collecting the heat in the hot utility air and extracting it therefrom in the second heat exchanger that is an air to air and/or water heat exchanger. The second heat exchanger can also be provided with means for water heating and comprises an auxiliary electrical heat element and a fan. This means that the power generation apparatus according to this embodiment of the invention can also provide hot air or hot water, since the second heat exchanger can be powered by electricity.
In the preferred embodiment the power generation apparatus includes battery charging means. The battery or batteries can be charged when the engine is running. This charging can be controlled automatically according to the load on the engine and the present demand for power at the power outputs of the power generation apparatuses, and the actual need for charging.
The internal combustion engine is in the preferred embodiment a diesel engine, but it is realised that other combustion engines, such as a petrol- or gas-driven engine or a gas turbine could be used alternatively.
In a second aspect of the invention the invention comprises a method of generating energy in a compact power generation apparatus, said method comprising the steps of combusting a fuel, such as diesel oil, petrol, gas or the like, from a fuel source in an internal combustion engine, converting the potential energy of the fuel into mechanical power is generated together with the generation of heat, converting said mechanical power into electrical power in a generator, and into an air flow through an air inlet and through and around the generator and the engine, absorbing the heat generated by the combustion in the engine and the generator in at least a part of the air flow, and extracting the heat in heat exchanging means and passing said heat on to a utility medium, such as air or water for utility purposes.
A method according to this aspect of the invention, enables the extraction of several sources of energy from a compact power generation apparatus in a consumable form, this means that the overall efficiency is increased, and that a compact power generation apparatus making use of this method becomes self-contained, as no external units must be connected to the generator in order to secure the supply of energy needed on the site.
In the preferred embodiment of the invention the at least one battery, such as a utility and/or a start battery is charged by the electrical power generated by the generator.
The electrical power generated by the generator is in a preferred embodiment converted into a utility AC voltage, such as 220/115 V AC, so that the power generation apparatus can substitute a normal power connected to the net of a household appliance, such as a coffee machine, a micro wave oven, etc. Preferably two further electric power outputs are present, providing 12/24 VDC 60/30 Amp for utility battery charging, and 12/24 VDC 10/5 Amp for start battery charging.
According to a method according to the invention, air conditioning can also carried out by electrically powered air conditioning means. This means that the temperature in a cabin or the like where the power generation apparatus is placed, can be controlled. A thermostat could also be connected to the control system of the power generation apparatus, making it possible to control the room temperature by altering between the use of an air conditioner and the air to air heat exchanging means. The heat exchange is done in two stages, such as described above: a first heat exchange is carried out extracting heat from the exhaust system and absorbing said heat in the air flow, and a second heat exchange is carried out extracting heat from the air flow and passing the heat on to the utility medium.
In a further aspect of the present invention a power management system and a method of automated power management of a compact power generation apparatus, such as a power generation apparatus and a method according to the previous described aspects. The method of automated power management comprises the steps of sensing the load on the engine, registering the demand for electrical and mechanical power, and feeding these measurements to a power management means involving computer means connected to regulation means, and regulating the power generation and distributing said available power according to the registered need for electrical power and mechanical power, respectively.
Hereby the power generation apparatus can be operated automatically facilitating the operation of the power generation apparatus.
According to a preferred embodiment of said method, the registration of the power demand includes registering the capacity of the at least one battery, and that available power is regulated according to the demand for electrical and mechanical power.
The power management can automatically and start and stop the engine according to present demands.
The invention further comprises a power management system for carrying out the method according to the third aspect of the present invention, where said system comprises sensor means for measuring the performance and/or characteristics of one or more energy conversion elements of the power generation apparatus, registration means for determining the presently required output of electrical and mechanical power from the power generation apparatus, and computer means for controlling one or more regulation means of the energy conversion means for adapting the kinds of generated power of the power generation apparatus according to the actual demands.
According to a preferred embodiment, the present power load on the generator is sensed, and that the power management according to the available power is determined according to a program containing a predetermined set of priorities. The power distribution can hereby be governed by a software in the computer. This software can be designed according to the area of operation, such as the climate, etc. that the miniature power generation apparatus is intended for.
The computer means preferably comprises a user interface for monitoring the power management and for entering user specified operation characteristics in the power management. Hereby it is possible to monitor the condition of the system, e.g. if a component is worn.
The power management system involves both electrical and heat power management, sensing the temperatures of the heat exchanging means and the air inlet of the power generation apparatus.